This invention relates to a hydraulic control system, and more particularly to a hydraulic control system for changing over the position of a spool depending upon an excitation current of a solenoid.
A conventional hydraulic control system is generally constructed in such a manner as shown in FIG. 1. More particularly, the conventional hydraulic control system includes a valve body 1 formed with a spool hole 2 and a spool 3 slidably arranged in the spool hole 2. Also, the hydraulic control system includes a connection member 4 provided on one side of the valve body 1 and a solenoid S0 fixedly mounted on the outside of the connection member 4.
The solenoid S0 includes a casing 5, a coil arranged in the casing 5, and a fixed core 7 and a movable core 8 arranged on the inside of the coil 6 in a manner to be in series in the axial direction thereof. The connection member 4 is formed into substantially the same diameter as the casing 5 and formed at the central portion thereof with a spring chamber 9.
The conventional hydraulic control system further includes a push rod 10 which is fittedly mounted at one end thereof on one side of the movable core 8. Also, the other end of the push rod 10 extends through the spring chamber 9 of the connection member 4 to the end surface of the spool 3, resulting in being contacted with the end surface of the spool. Such construction causes the push rod 10 to force the spool 3 depending upon an excitation current of the solenoid S0.
The valve body 1 is formed on the side thereof facing the casing 5 with a positioning hole 11 serving as an accessory port. In the positioning hole or accessory port 11 is received an accessory such as a port relief valve or the like for selectively carrying out the communication between a return passage 12 and an actuator passage 13 each formed in the valve body 1.
In the conventional hydraulic control system constructed as described above, when an accessory such as a relief valve or the like is to be positioned in the positioning hole 11, the accessory and the connection member 4 interfere with each other. Thus, the conventional hydraulic system fails to successfully mount the accessory through the positioning hole 11 on the valve body 1.
In order to eliminate such a disadvantage, it is proposed to increase the length of the push rod 10 to secure a space sufficient to permit the accessory to be mounted therethrough on the system. Unfortunately, this causes an excessive increase in length of the push rod 10, resulting in the push rod 10 being obliquely deflected from the axial direction thereof when the push rod 10 is moved depending upon excitation of the solenoid. This leads to a failure in actuation of the solenoid.
Also, an excessive increase in length of the push rod 10 causes further disadvantages such as deformation of the push rod such as bending and damage of the push rod during transportation or the like.